In another application by the same inventors (0502872.5), an improved means of achieving the desired separation of adjacent vertebral processes is provided in the form of a tapered segmented screw-like device which can be deployed using minimally invasive surgical techniques known to those skilled in the surgical art. It is the object of the present invention to provide a further improved means of separating the adjacent vertebral processes which has a minimal cross-sectional profile during insertion so that both the time taken for the surgical procedure, and the trauma caused by the procedure, are further reduced. In addition, the manufacture of the present invention is less complex and therefore less costly than that of the device described in the above mentioned previous application.